The present invention is related to conjugate fibers and nonwoven fabrics made therefrom. More particularly, the invention is related to conjugate fibers, which contain at least two olefin polymers having different melting points, and pattern bonded nonwoven fabrics made therefrom.
Pattern bonded nonwoven fabrics produced from thermoplastic fibers are known in the art and have found uses in a variety of applications, especially in disposable articles. A pattern bonded nonwoven fabric contains a pattern of bonded points or regions in which the fibers in the bonded regions are compacted under heat and pressure to autogenously fuse the polymer exposed on the surface of the fibers and form interfiber bonds. Although nonwoven fabrics are highly suitable for many applications, they tend to be stiff and paper-like when compared to woven textile fabrics of similar basis weight. The stiff property of nonwoven fabrics is perceived to be disadvantageous, particularly, in applications where the fabric comes in contact with the human skin, such as surgical drapes, diapers, sanitary napkins, incontinence care products and disposable garments. Many attempts have been made to produce soft nonwoven fabrics, e.g., changing bond patterns, incorporating a softening agent in the composition of nonwoven fabrics and applying a topical softening agent on nonwoven fabrics. For example, U.S. Pat. No. 3,855,046 to Hansen et al. teaches a point bonded soft and drapable nonwoven fabric that contains releasably bonded regions. U.S. Pat. No. 3,973,068 to Weber teaches a soft nonwoven web that is produced from a thermoplastic polymer composition containing a latent lubricant. The presence of the lubricant reduces the tendency of secondary bond formation outside the bonding regions during the bonding process and results in improved softness and drapability without adversely affecting web strength properties.
Another approach known in the art for producing a soft nonwoven fabric is fabricating a nonwoven fabric from crimped conjugate fibers. Such crimped conjugate fibers contain at least two component polymers that occupy distinct cross-sections of the fibers, typically in a side-by-side configuration. In general, the component polymers for crimped conjugate fibers are selected from polymers having different shrinkage properties, thereby the shrinkage differential between the component polymers causes crimps in the fibers during or subsequent to the fiber spinning process. Typically, the component polymers additionally are selected to have different melting points, and the lowest melting polymer thereof is exposed on the peripheral surface along the entire length of the fibers. The exposed low melting polymer is utilized to improve the bondability of nonwoven webs produced from such conjugate fibers. After the conjugate fibers are deposited or carded to form a nonwoven web, the exposed lowest melting polymer is utilized to form interfiber bonds, especially at crossover contact points of the fibers. When the fabric is heat treated to a temperature above the melting point of the lowest melting polymer but below the melting point of the other component polymers of the fibers, the lowest melting polymer is rendered tacky or adhesive and forms interfiber bonds while the other component polymers maintain the physical integrity of the nonwoven fabric. However, the bondability of such conjugate fiber fabric is improved at the expense of other properties including abrasion resistance since the bond points formed from the lowest melting component polymer tend to exhibit a lower abrasion resistance than those formed from higher melting polymers.
Although the above-described approaches of producing soft, drapable nonwoven fabrics are highly useful, there still remains a need to produce a bonded nonwoven fabric that has improved desirable properties, such as softness, drapability, abrasion resistance and the like, and that does not require additional manufacturing steps to attain such desirable properties.